update authors list for 2.8.3 and add a log command to the howto

HOWTORELEASE.rst

@@ -8,7 +8,9 @@ Note: this assumes you have already registered on pypi.
 2. Check and finalize CHANGELOG
 
 3. Write doc/en/announce/release-VERSION.txt and include
-   it in doc/en/announce/index.txt
+   it in doc/en/announce/index.txt::
+
+        git log 2.8.2..HEAD --format='%aN' | sort -u # lists the names of authors involved
 
 4. Use devpi for uploading a release tarball to a staging area::
 

doc/en/announce/release-2.8.3.rst

@@ -15,13 +15,17 @@ As usual, you can upgrade from pypi via::
 
 Thanks to all who contributed to this release, among them:
 
-    Bruno Oliveira
-    Demian Brecht
-    Florian Bruhin
-    Ionel Cristian Mărieș
-    Raphael Pierzina
-    Ronny Pfannschmidt
-    holger krekel
+        Bruno Oliveira
+        Florian Bruhin
+        Gabe Hollombe
+        Gabriel Reis
+        Hartmut Goebel
+        John Vandenberg
+        Lee Kamentsky
+        Michael Birtwell
+        Raphael Pierzina
+        Ronny Pfannschmidt
+        William Martin Stewart
 
 Happy testing,
 The py.test Development Team